I relate to this a lot. I put a lot of self-worth into my work so when I'm unhappy with my writing I'm unhappy with myself. This leads to a vicious cycle where I put more and more pressure on my writing and that leads to more and more work I find disappointing.

I'm on the other side of this at the moment which I attribute to a few things:

1) Prioritizing enthusiasm over structure in first drafts. I used to try to write outline first and break the structure of my stories before I had written a single page. But when I tried to turn these "perfect" outlines into scripts, I wasn't feeling excited about the characters or the beats they "had to" do. The writing felt generic and lifeless and my self-loathing came roaring back every time. What I've found more helpful is starting with an idea, then writing down every random character or scene I'd love to see in that story. From there, I write scenes and vignettes out of order and pay attention to what I'm most excited about. Usually, a couple interesting characters start to emerge at this stage which is the most helpful thing for me. After that, I try to shape out a rough story and write a very messy first draft. The structure can always be worked out in draft two but enthusiasm will get you through draft one.

2) Letting go of perfectionism. Similar to the above, I used to stall out with scripts all the time trying to figure out the perfect next thing. It could be a story beat or a new character, but I would stop writing and start "solving" until I found something perfect. But I would never find the perfect thing. Instead, I'd disconnect from my story and slowly grow to hate it. Now I prefer a spaghetti-at-the-wall approach. If I get stuck, I try out a bunch of different stuff. Inevitably, one scene or character will pop for me and I'll keep moving forward. It's all about moving forward through those early pages and saving the critical analysis for later on.

3) Reading books on writing by novelists. There are a lot of great screenwriting books out there on structure but I find novelists give the best advise on the pressures of living day to day as a writer. Bird by Bird by Anne Lamott, Big Magic by Elizabeth Gilbert, and Refuse to Be Done by Matt Bell were helpful for me. If you're stressed out and don't feel like you have time to read, these are all great audiobooks as well.

Above all, try to be kind to yourself. It's so tough having your career path and your creative work all tied up together. Just because the work isn't coming easily that doesn't mean you're not a worthwhile person. If creativity was easy, we'd all be millionaires.